This invention relates to a method of producing polycrystalline semiconductor material, and, more particularly, to a method of producing polycrystalline ribbons of silicon.
Semiconductor devices are generally fabricated from wafers of monocrystalline silicon. Various procedures for preparing monocrystalline silicon wafers have been described in the prior art. Thus, the Czochralski method comprises pulling a monocrystalline rod from a pool of liquid produced by melting polycrystalline silicon. Another method, known as the float zone technique, comprises pulling a monocrystalline rod from a liquid region, formed by localized heating, within or on top of an ingot of polycrystalline material. Both techniques produce a monocrystalline rod which must be sawed into slices and further processed by lapping, polishing, and/or etching to produce wafers suitable for the production of semiconductor devices.
With the present need for new energy sources, many suggestions have revolved around the use of solar energy. One way of utilizing this type of energy is with solar cells, whereby radiant solar energy is converted directly to electrical energy. However, systems using solar cells will require large amounts of semiconductor material, that is, monocrystalline silicon. If such systems are to become commercially acceptable, such slicon must be attainable at a cost far less than present costs for monocrystalline silicon wafers.
In the aforementioned related application, a method of producing a polycrystalline silicon web has been disclosed. In accordance with that invention, a particulate layer of polycrystalline silicon in contact with a continuously moving belt is exposed to a heat source which melts its upper surface to form a coherent polycrystalline web. The web of polycrystalline semiconductor material thus obtained can then be converted into monocrystalline material, for example by contacting it with a monocrystalline semiconductor material seed and heating the interface therebetween as described in copending application U.S. Ser. No. 537,976, filed Jan. 2, l975, entitled, "Silicon Manufacture" and assigned to the assignee of the present invention.